Heat-sensitive copy-sheet



United States Patent 3,129,109 [EAT-SENSITIVE COPY-SET Wesley R. Workman, St. Paul, Minn, assignor to Minnesota Mining and Manufacturing Company, St. Paul, Minn, a corporation of Delaware No Drawing. Filed Sept. 25, 1961, Ser. No. 140,236 7 Claims. (Cl. 117-36.S)

This invention relates to copy-sheet materials useful in the copying of graphic originals having differentially radiation-absorptiveimage and background areas, by a thermographic copying process involving the brief intense irradiation of said original while in heat-conductive contact with said copy-paper. In its preferred form the invention relates to uncolored, essentially white heatsensitive copy-sheets which are rapidly and permanently converted to visibly distinct colored form when locally heated in the thermographic copying process or by momentary contact with a metal test bar at a conversion temperature within the range of about 90-l50 C.

It has now been found that essentially white heat-sensitive copy-sheets which retain their clean white appearance and full sensitivity to thermographic copy tempera tures under normal storage and use conditions, and which provide copies having dense, high contrast image areas in any of a considerable variety of desired colors, may be produced by including in the heat-sensitive layer as the essential color-producing inter-reactants a Z-aminothiazole and an N-chloro organic oxidizing agent.

The reactants are preferably maintained in uniform distribution and in close juxtaposition in a thin bonding layer of a film-forming polymeric or resinous binder, either as a thin self-sustaining film or as a reactant layer on a paper-like supporting substrate. The two reactants may be intermixed and included within a single layer, or may be separately applied in two contacting layers on a single substrate or as separate sheet materials which are subsequently placed in temporary face-to face relationship during the copying step.

A preferred form of heat-sensitive copy-sheet prepared in accordance with the principles of the invention is represented by the following symbolic diagram:

Visibly heat-sensitive layer containing a Z-aminothiazole and an N-chloro organic oxidizing agent Paper-like backing The reactants may be separately dispersed in separate binder solutions, using binder and solvent systems in which neither reactant is soluble, and blending the two dispersions just prior to coating on paper or other substrate. in some instances one or the other of the reactants may be soluble in the solvents employed. Where both reactants are soluble, premature reaction frequently occurs; this can be avoided by proper selection of binders and solvents, by separate application and intermediate drying of the two layers, or in other Ways. The binder must also be so selected as to be inent to, or non-reactive with, the color-forming reactant components. Typical binders which have been found useful in these copy-sheet formulations include styrene-isobutylene copolymer, polyvinyl acetate, cellulose acetate, vinyl chloridevinyl acetate copolymer, polyvinyl butyral, polycarbonate and polystyrene polymers.

9 The color-producing layer may contain other materials where desired for specific purposes. Pigments, e.g. zinc oxide, titanium dioxide, carbon black, toluidine toner, Prussian blue, may be added for increased opacity, or to provide partial absorption of radiation in the copying process, or to impart a desired tint to the sheet or com pensate for an undesired tint, or for other purposes. Fillers, for example calcium carbonate, magnesium carbonate, powdered glass, starch and asbestine, may be included, e.g. as diluents or to provide improved surface properties. Dyes, softeners and plasticizers, waxes and resins, and many other materials may be added. Additional coatings or layers may also be provided where desired. For example, clear transparent surface protective layers impart resistance to moisture absorption and to abrasion; pigmented opaque or colored layers are useful in providing desirable background appearance or improved contrast; impregnants or coatings may be applied to film or paper substrates for increased strength, resistance to moisture or solvents, improved bonding of heatsensitive layer, or other purposes.

Typical of the 2-aminothiazole reactants which have been found useful in the practice of the invention are 2-amino-5-nitrothiazole, Z-aminobenzothiazole, 2-amino 6-methylbenzothiazole, 2-amino-4t(4'-biphenylyl)thiazole, and 2-aminonaptho(l,2)thiazole. The last-named compound is particularly eifective in providing a highly stable copy-sheet which is sensitive to moderate copying temperatures and yields a pleasing blue-black image on a white background. These compounds have in common the normally stable aminothiazole structure wherein the radical or radicals attached to the free valence bonds on the doubly bonded carbon atoms are stable and resistant to oxidation. Pyridine or quinoline ring structures are particularly effective, as are the specific radicals of the exemplary reactants just named. Other normally solid and substantially colorless stable aminothiazole compounds having the same basic structure are likewise useful in the practice of the invention.

As the second essential reactant there is employed a normally solid and substantially colorless organic oxidizing agent having a positive halogen atom attached to a nitrogen atom, as exemplified by such compounds as:

N,N' bis(m nitrobenzenesulfonyl) N,N' dichloroethylenediamine;

N,N' bis (p toluenesulfonyl) N,N' dichloroethylenediamine;

N,N' dichloro N,N diphenylbiphenylsulfone 4,4-

disulfonamide;

The N-chlorobenzenesulfon-anilides; and trichloromelamine.

The amounts of reactants may be widely varied and need not be in stoichiometric relationship, the only requirement being that suflicient oxidizing agent and sufiicient aminothiazole be present, and in sufiiciently intimate and uniform juxtaposition, to produce a sufi'icient quantity and concentration of the colored reaction product at the heated areas so as to provide an image of required visibility.

The following examples will serve further to illustrate but not to limit the invention.

Example 1 Map overlay tracing paper is coated using a knife coater to apply a 3-mil layer of a solution of 0.16 g. of G-inethyl-Z-aminobenzthiazole, 1 g. of vinyl chloridevinyl acetate copolymer (Vinylite VYHH) and 9 g. of awtone. After drying, a 3 mil top coat of 2.18 g. of N,N' bis(p-toluene-sulfonyl)-N,N'-dichloroethylenediamine dispersed in a solution of 5 g. of styrene-isobutylene copolymer (parapol) in 45 g. of heptane is applied. A white, heat-sensitive copy-paper results from drying this film. This copy-paper may be used for preparing copies of differentially radiation-absorptive graphic 7 C9 originals by thermographic copying processes. Such copies consist of purple images on white backgrounds and are stable on storage in high humidity, light and at moderate temperatures.

Similar copy-papers may be prepared in which the film-forming binder for the Z-aminothiazole is ethyl cellulose, polyvinyl butyral, polystyrene (dissolved in acetone and toluene), polycarbonate resin (dissolved in dioxane), or a mixture of equal parts polyvinyl acetate and cellulose acetate. For maximum stability, the oxidant should be coated as a dispersion, such as may conveniently be prepared by prolonged ball milling.

Example II Map-overlay tracing paper is coated with a 4.5 mil layer of a dispersion consisting of 2.6 parts of 2-aminonaphtho(1,2)thiazole, 3.3 parts benzoin, 3.3 parts N,N'- bis(m nitrobenzenesulfonyl) N,N'-dichloroethylenediamine, 10 parts Parapol, and 90 parts heptane by means of a knife coater. Drying forms a heat-sensitive copypaper requiring slightly higher conversion temperatures than the copy-sheet of Example I. Copies prepared with this sheet have intense blue-black images on a white background.

A similar sheet prepared without benzoin required a slightly higher temperature for color development but had improved stability towards moderate heat, humidity and light.

Replacement of 2-aminonaphtho(1,2)thiazole with 2- aminobenzothiazole results in a white copy-paper having a lower conversion temperature. The copy is in the form of brown images on a white background.

Example III Sturdy white paper is treated with a dilute solution of 2-aminonaphtho( 1,2)thiazole in methanol and then dried. An acetone solution of trichloromelamine is applied to map-overlay tracing paper and the paper dried. The uncoated side of the latter sheet is supplied with a differentially radiation-absorptive image pattern by printing thereon with India ink. The sheets are placed with their coated surfaces in heat-conductive pressure-contact and the printed surface is briefly exposed to intense radiant energy in accordance with the thermographic copying process. A blue-black image forms on the sturdy white paper. Several subsequent copies on other pieces of similarly treated sturdy white paper may be made using the same printed treated original.

What is claimed is as follows:

1. A heat-sensitive copy-sheet product useful in the copying of differentially radiation-absorptive graphic originals by the thermographic copying process, said copy-sheet including a heat-sensitive layer containing in uniform intimate juxtaposition inter-reactant image-forming components consisting of a normally stable 2-aminothiazole having the structure S II C land an organic oxidizing agent having a positive halogen atom attached to a nitrogen atom.

2. A heat-sensitive copy-sheet product useful in the copying of difieren-tially radiation-absorptive graphic originals by the thermographic copying process, said copy-sheet comprising a paper-like substrate and a substantially colorless visibly heat-sensitive coating thereon containing in uniform intimate juxtaposition inter-reactant image-forming components consisting of a normally solid colorless normally stable Z-aminothiazole having the structure and a normally solid colorless organic oxidizing agent having a positive chlorine atom attached to a nitrogen atom.

3. A visibly heat-sensitive copy-sheet product having a heat-sensitive layer of uniformly intimately juxtaposed inter-reactant components consisting of a normally solid colorless organic oxidizing agent having a positive chlorine atom attached to a nitrogen atom, and 2-amino-5- nitrothiazole.

4. A visibly heat-sensitive copy-sheet product having a heat-sensitive layer of uniformly intimately juxtaposed inter-reactant components consisting of a normally solid colorless organic oxidizing agent having a positive chlorine atom attached to a nitrogen atom, and Z-aminobenzothiazole.

5. A visibly heat-sensitive copy-sheet product having a heat-sensitive layer of uniformly intimately juxtaposed inter-reactant components consisting of a normally solid colorless organic oxidizing agent having a positive chlorine atom attached to a nitrogen atom, and 2-amino-6- methylbenzothiazole.

6. A visibly heat-sensitive copy-sheet product having a heat-sensitive layer of uniformly intimately juxtaposed inter-reactant components consisting of a normally solid colorless organic oxidizing agent having a positive chlorine atom attached to a nitrogen atom, and 2-amino-4(4- biphenylyl)thiazole.

7. A visibly heat-sensitive copy-sheet product having a heat-sensitive layer of uniformly intimately juxtaposed inter-reactant components consisting of a normally solid colorless organic oxidizing agent having a positive chlorine atom attached to a nitrogen atom, and Z-aminonaphtho( 1,2)-thiazole.

References Cited in the file of this patent UNITED STATES PATENTS 

1. A HEAT-SENSITIVE COPY-SHEET PRODUCT USEFUL IN THE COPYING OF DIFFERENTIALLY RADIATION-ABSORPTIVE GRAPHIC ORIGINALS BY THE THERMOGRAPHIC COPYING PROCESS, SAID COPY-SHEET INCLUDING A HEAT-SENSITIVE LAYER CONTAINING IN UNIFORM INTIMATE JUXTAPOSITION INTER-REACTANT IMAGE-FORMING COMPONENTS CONSISTING OF A NORMALLY STABLE 2-AMINOTHIAZOLE HAVING THE STRUCTURE 